The present invention relates to a feeder of molten metal for moulds of continuous casting machines of products of small thickness, and more precisely, to a feeder of molten metal for moulds in continuous casting machines which is apt to feed the molten metal in the mould in a uniform manner and transversally to the mould itself.
Continuous casting machines of molten metal are known which comprise a mould delimited by a pair of cylindrical counter-rotating rollers with horizontal axes and lying or not on a same horizontal plane, and by two side containment end members contacting the end portions of said rollers.
Said rollers are generally metallic and cooled inside through circulation of a refrigerant liquid under pressure (water for example) and spaced in order to allow continuous casting from the mould of a solidified body which has a thickness and a width approx. equal to the length of the rollers where the solidification takes place.
Furthermore, the so-described mould is provided to be fed by a feeder of molten metal connected to a tundish above the mould.
Great effort has been made up to now by the greatest steel manufacturers and installers to solve the several problems connected with the continuous casting of thin thicknesses of alloy steel, in particular stainless and magnetic, the quality thereof depends, among other things, on the superficial perfectness of the cast body.
In fact, among the most important causes of surface defectiveness in a continuously cast product is the lack of uniformity in the distribution of the molten metal in the mould. Said lack of uniformity causes differences in the temperature and material flow which, in turn, influence the cooling speed and the thickness of the cast product as well as its structure and superficial homogeinity.
In particular, changes in the material flow and temperature lead to the following problems:
a) superficial waving, which determines a non-horizontal curve of the points where the solidification starts with subsequent lack of uniformity in temperatures of the casting product which encourages the increase in the superficial defectiveness, i.e. the increase in the density of cracks and superficial roughness;
b) non-homogeneous distribution of the temperature in the mould, which causes longitudinal oscillations in thickness, also called depressions.
The above-mentioned problems are much more felt in case of continuous casting of thin products. In fact, given the small dimensions of moulds, it is difficult to control the flow and the related turbolences as well as the temperature distribution.
Different methods and devices have been devised for this purpose. In NL-A-8801101 a frustum of pyramid is applied on the bottom of an immersion pipe, but the walls of the pipe do not diverge from each other downwards in the lower portion thereof. In JP-A-03027847 is disclosed a submerged nozzle wherein the walls of the lower portion converge toward each other downwards.
The EP patent 515 075 illustrates a method and an apparatus of continuous casting of thin metal products.
According to the above mentioned patent, the apparatus includes a feeder of molten metal to the mould comprising an inlet duct for the molten metal extending to an outlet opening of the molten metal. The feeder is characterized in that said duct has a curved side surface apt to eliminate possible turbolences and discontinuities of the molten metal flow in the mould therebelow.
Said solution appears on one side excessively complex from a mechanical point of view, in view of the need of having a tundish integrally connected to a weir and to a cleft plunger. On the other side, it does not show good functional requirements, such as the semplicity in the construction of the feeder, the great reliability, the easy handling, the ease in the pre-heating of the feeder both when mounted and out of line and the possibility of moving it, while hot, for operation.
The present invention overcomes all the above-mentioned disadvantages. It is in fact object of the present invention to provide a feeder of molten metal for moulds of continuous casting machines comprising a cylindrical body, within which a main outflow duct of the molten metal coming from the tundish is formed to which the cylindrical body is connected by means of a frustoconical joint, formed integrally with the cylindrical body at the upper end thereof, characterized in that the free end of the cylindrical body is frustopyramid in shape with at least two sloping walls diverging from each other downwards and has a plurality of outlets communicating with the main outflow duct.
Further, according to the present invention, each sloping wall forms an angle with the longitudinal axis of the feeder comprised between 10xc2x0 and 45xc2x0.
Furthermore, according to the present invention, at least two outlets of said plurality of outlets have their longitudinal axis forming an angle with the longitudinal axis of the feeder comprised between 0xc2x0 and 95xc2x0 and, preferably, between 65xc2x0 and 95xc2x0.
Furthermore, according to the present invention, the base of the frustopyramid-shaped free end of the feeder can be plane or convex.
Furthermore, according to the present invention, at least a portion of the longitudinal axes of said plurality of outlets and the longitudinal axis of the feeder lie on the same plane.
In case, according to the present invention, at least two outlets of said plurality of outlets have their longitudinal axes forming an angle with the longitudinal axis of the feeder comprised between 0xc2x0 and 90xc2x0 and each of said longitudinal axes lies on a plane orthogonal with the plane containing the longitudinal axes of the remaining outlets and of said feeder.
Furthermore, according to the present invention, the feeder has optionally the base of its free end having at least one cleft shaped outlet.
Furthermore, according to the present invention, the feeder is characterized in that it is made of refractory material chosen among the group comprising: silicon dioxide, graphite alumina and zirconium-coated graphite alumina.
The present invention also refers to the use of the feeder according to claims 11 and 13.
The present invention will be illustrated in greater detail in the following by a description of various preferred embodiments thereof, given as a non-limiting example and with reference to the enclosed drawings.